The aim of this project is to study the reflex mechanisms involved in pulmonary reflexes. This study will link previous efforts by the Principal Investigator on J receptor reflexes. In order for us to understand the central mechanisms that are involved in the control of breathing it is necessary to unravel some of the neuronal networks that exist in the brain stem and which are under control of peripheral receptors from the lungs and other intrathoracic structures. In this project we address ourselves to this problem and with the use of recently developed neuroanatomical techniques we intent to trace pathways of known physiological significance into the nervous system. We also intend to study the connections of some of the brain stem regions that are involved in the control of respiration. The caudal portion of the brain stem which is concerned primarily with expiratory function will be studied using the retrograde transport of horseradish peroxidase. This will be the first attempt made to study the neural control mechanisms of respiration in this manner. A considerable emphasis will be placed on the physiological function of the region under study before any anatomical questions are asked. The principal investigator is interested in vagal afferents and central respiratory interactions and this project will also be involved in assessing the role played by various pulmonary afferents in the control of repiration. In essence this project addresses the question: How do vegal affernts exert their influence on respiratory neural mechanisms and where is this information processed?